SPONGE BATH: A 1925 photo depicts a child being given a bath in a Neptune's Cup sponge. (Photo: Public domain)

It's the sponge that takes the idea of a sponge bath to a whole new level: the giant Neptune's Cup. First discovered in 1822, these sponges once grew so large that they were commonly used as bath tubs for children. However, that handy use quickly led to overharvesting, and the last time anyone saw one alive was in 1908. Many believed the sponges had become extinct.

That was until March of this year, when biologists doing a routine survey dive along Singapore's coast spotted something that none of them could immediately identify. Of course they couldn't: a living Neptune's Cup sponge hadn't been spied for more than 100 years.

But there it was — two of them, in fact, just 50 meters from one another. Sponge expert Lim Swee Cheng, author of the book "A Guide to Sponges of Singapore," was called in to confirm the finding, according to a report by Scientific American.

"My heart skipped a beat when I saw it in Singapore waters this year," Lim recently wrote on his Facebook page, after positively identifying the sponges as Neptune's Cups.

With diameters measuring 30 centimeters across, the pair of newly discovered sponges are tiny compared to legend, which described heights of more than a meter and diameters wide enough to hold a bathing human. These new discoveries are just babies, say scientists — but they are growing fast. And their presence may indicate that a more stable population exists nearby.

"The presence of two young Neptune's Cup sponges within a surveyed area of 50m by 50m signals hope that more are present within the area," said marine biologist Karenne Tun, one of the scientists to rediscover the species. "More importantly, [it] points to the possibility of adult populations present within Singapore's coastal waters."

Finding this pair of live specimens also means that scientists can study their ecology for the first time, as well as learn about how they can be conserved.

"Now we have the opportunity to study the biology and ecology of this impressive sponge and learn about its life cycle," said Tun. "We've already had the first surprise: The Neptune's Cup was thought to be a very slow-growing species. However, between our last visits in April and August, respectively, it had grown several centimeters. Looks like we might have to rethink some of these ideas."